Syntheses, crystal structures, optical and thermal properties of two new zirconium polyselenides (K8Zr6Se30) containing one-dimensional anionic chains

Two new ternary compounds with composition K8Zr6Se30 were prepared by react ing zirconium powder in potassium polyselenide melts. Both compounds crysta llize in the triclinic space group P (1) over bar with a = 12.391(1) Angstr om, b = 14.897(2) Angstrom, c = 15.253(2) Angstrom, alpha = 73.149(9)degree s, beta = 76.330(9)degrees, gamma = 70.023(9)degrees and V = 2502.8(3) Angs trom (3) for I and a = 12.2793(8) Angstrom, b = 14.887(1) Angstrom, c = 22. 512(2) Angstrom, alpha = 72.714(7)degrees, beta = 88.475(7)degrees gamma = 70.748(7)degrees and V = 3698.1(4) Angstrom (3) for II. Their structures co nsist of infinite linear one-dimensional anionic chains running parallel to [110], which are connected by the potassium cations. The structural differ ences between both compounds originate from some disordering in one of the two crystallographically independent anionic chains of each compound, in wh ich Se2- anions are exchanged by Se-2(2-) anions to some degree. The optica l band gap was determined by UV/Vis reflectance spectra to 1.91 eV for I an d 1.81 eV for II. Differential scanning calorimetry investigations show, th at II decomposes reversibly at about 500 degreesC to K2Se3 and ZrSe3. On co oling II is formed again. These results are confirmed by the direct reactio n between K2Se3 and ZrSe3 which leads directly to II.